Influence of Bondcoat Surface Treatment on Thermally Grown Oxide and Lifetime in Suspension Plasma Sprayed Thermal Barrier Coatings

Thermal barrier coatings (TBCs) are a vital component of gas turbine engines in power generation and aerospace applications. By using suspension plasma spraying (SPS), a porous columnar TBC microstructure can be produced that can combine the advantages of conventionally used electron beam – physical vapour deposition (EB-PVD) and atmospheric plasma sprayed (APS) coatings, that is low thermal conductivity and high durability along with low cost. Improvements in lifetime of SPS TBCs that enables its widespread commercialisation would result in huge cost savings as well as lower emissions due to higher engine efficiency.

Lifetime of a TBC system is significantly dependent on topcoat-bondcoat interface and bondcoat treatments as they influence the growth rate of thermally grown oxide (TGO) layer as well as the mismatch stresses generated in the topcoat during thermal cyclic testing. In this work, the effect of shot peening, grit blasting and vacuum heat treatment on TGO growth rate and lifetime in SPS TBC systems was investigated. Commercial NiCoCrAlY bondcoat powder was deposited by high velocity air fuel spraying while axial-SPS was used for topcoat deposition using identical spray parameters for all samples. The influence of changes in topcoat-bondcoat interface topography on oxide growth and lifetime will be discussed.